This invention pertains to the alignment of patterns, such as the alignment of electrical circuit patterns which are to be placed on the opposite sides of a double-sided printed circuit board.
In the field of electronics, so-called printed circuit boards are in relatively widespread use. These boards are typically formed of a thin sheet-like insulative web, on one or both sides of which are strips of conductive material which form an electrical circuit pattern adapted to receive various electrical components that are mounted on the board. Where double-sided printed circuit boards are used, i.e., those wherein conductive circuit patterns exist on opposite sides of the board, alignment of the patterns (on the opposite sides of the board) is critical.
A typical double-sided printed circuit board, before it has any circuit patterns thereon, takes the form of a thin, sheet-like insulative web, on the opposite sides of which are bonded layers of a conductive material, such as copper. Circuit pattern layouts for the two sides of the board are prepared in a suitable manner, and photographic reproductions of these layouts are then made which are employed in a photo-etching process to remove copper from the two layers on the board selectively so as to leave on the opposite sides of the board the desired circuit patterns.
In the past, the problem of producing proper reverse-side alignment of these pattern layouts has been solved through the use of relatively expensive jigs and the like, and through time-consuming and costly techniques such as the drilling of alignment holes, and the use of alignment pins in conjunction with such holes and jigs.
A general object of the present invention is to provide a novel method for facilitating reverse-side alignment of such pattern layouts, which method can be performed simply, quickly, and without the use of costly and elaborate equipment.
The method of the invention rests on the concept that a pair of intersecting edges in a particular circuit board may be used as a guide for promoting pattern alignment. Simply stated, the method proposes first, and after completion of photographic pattern templates or layouts by conventional techniques, the placing of such templates in aligned, confronting relationship, as by setting the templates face-to-face against each other and shifting them relative to one another until the patterns thereon are properly aligned. This can easily and quickly be done by hand and by looking through the usual photographic pattern negatives to confirm alignment. Preferably, a releasably gripping adhesive is used in the space between the confronting faces, and the aligned templates are temporarily stuck together.
Following alignment of the templates as just described, a pair of intersecting margins therein are trimmed to produce an angle of intersection therebetween which matches the angle of intersection of a pair of selected edges in the board onto which the patterns of the templates are to be placed. The trimmed templates are then separated, and suitably fitted on opposite sides of the board, with their "trimmed" edges flush with the two selected intersecting edges of the board. Photo-exposure, developing and etching of the board is then performed in a conventional manner.
Through utilizing this technique, it will be obvious that extremely accurate reverse-side pattern alignment can be achieved. Further, it will be obvious that such alignment can be achieved in an extremely quick and simple manner, and without the necessity of using expensive alignment equipment.
These and other objects and advantages which are attained by the invention will become more fully apparent as the description which now follows is read in conjunction with the accompanying drawings.